Abstracts

Material-specific memory differences in temporal-lobe function have been well established, with converging evidence from neuroimaging and lesion studies. A strong assumption is that the processes underlying verbal and figural memory, particularly as they relate to the medial temporal lobe (MTL), are similar except for the type of material to be learned. However, questions have been raised whether other issues, such as novelty versus familiarity of memoranda, are related to differences in how the two temporal lobes process information (1997). The goals of this fMRI study were to assess potential processing differences in the MTL as a function of stimulus type at both the encoding and retrieval stages of memory, and to study the role of stimulus familiarity in these processes., Sixteen neurologically-healthy subjects were asked to learn four types of visually-presented material: abstract designs (figural, unfamiliar), drawings of real objects (figural, familiar), nonsense words (verbal, unfamiliar), and abstract real words (verbal, familiar). Subjects were scanned during two encoding trials, two recognition trials, and a 20-min delayed recognition trial., Overall, a processing difference was observed in encoding compared to recognition and for verbal versus figural material. Encoding: BOLD activation decreased on the second encoding trial in the posterior hippocampus and parahippocampal cortex, especially on the left. The difference was most significant for verbal material. In contrast, activations were maintained on the second trial in these regions when encoding figural material. Recognition: During recognition, greater activations for figural than for verbal material were observed in posterior hippocampus and parahippocampal cortex. In addition, there were differences in side and region as a function of stimulus type: activation was greater for figural than for verbal material in the right anterior hippocampus, but greater for verbal than figural material in the left perirhinal cortex. There were no effects of novelty versus familiarity of stimulus type., There are dissociations among different regions in the left versus the right medial temporal lobe depending upon whether one is initially learning new material or retrieving learned material, and whether such material is verbal or figural. These relationships are more complex than suggested by the traditional notion of material-specific lateralization, and support the idea that there are significant processing differences between the left and right temporal lobes.
Jones-Gotman et al. Neuropsychologia (1997);35:963-73., (Supported by the Canadian Institutes of Health Research.)